Search for Blazar Flux-Correlated TeV Neutrinos in IceCube 40-String Data

Transcription

1 Search for Blazar Flux-Correlated TeV Neutrinos in IceCube 40-String Data Derek Fox, Colin Turley Fourth AMON Workshop 4 December 2015 Penn State

2 2 Background and Outline Two models for blazar emission: hadronic and leptonic Hadronic models robustly predict associated TeV neutrinos (proportional to TeV flux) AMANDA-II detected a neutrino from the vicinity of 1ES during a TeV orphan flare, though no association claimed, significance not quantifiable Neutrino observations of blazars should ultimately distinguish models: Hadronic or leptonic for base emission? Flares? TeV orphan flares?

3 3 The IceCube 40-String Search Collected between April 2008 and May 2009 Public since 2011 Detected upgoing neutrino events (atmospheric/cosmic ray air shower dominated) IceCube team analysis revealed no point sources (IceCube+11) Blazars are not steady sources... Every neutrino detected by IceCube in its 40 string configuration, plotted in a mollweide projection.

4 4 Blazar Light Curves VERITAS TeV blazar monitoring over IC40 Data are not public (VERITAS collaborative project) We will illustrate the approach here using public data TeV gamma ray light curves for three blazars. These graphs compile public data from several observatories, including VERITAS. The data was obtained at

5 5 Interpolation A linear (red) and spline (green) interpolations for Mrk 421 VERITAS public data Idea: Leverage TeV data, integrate on each blazar only when it is TeV-bright Requires defining temporal periods of interest for each blazar Linear interpolation: Simple but unphysical, esp. with long gaps Spline fitting: Poorly motivated, range violations common

6 6 Interpolation via the Gaussian Process Regression (GPR) GPR: assume data can be reproduced as normally distributed samples from a process with stationary mean and covariance First pass: Analyze data to determine mean and covariance Second pass: Predict function values at arbitrary intermediate points (with confidence regions) GPR on Mrk 421 VERITAS public data (ML in green, 90%-c.i. in blue)

7 7 Interpolation via the Gaussian Process Regression (GPR) Beyond a few correlation lengths, the GPR reverts to the mean function for its max likelihood, and to the data range for confidence intervals Work in log space to reduce heteroskedasticity Force the mean function to the blazar baseline flux Use the Python package pygps and work only with ML light curve GPR on Mrk 421 VERITAS public data (ML in green, 90%-c.i. in blue)

8 8 Selecting Times of Interest Work with complete ML light curve for each blazar (spanning IC40) Select the brightest fraction of points Maximize ratio of TeV fluence to number of neutrinos needed to give a 3σ excess over atmospheric background Fraction of fluence vs. time for Mrk 421 (left). The green line shows constant fluence. Optimization selected the brightest 80 days, shaded to the left, and also shown below.

9 9 Optimization with the Proprietary VERITAS Data Markarian 421 bright intervals dominate the optimization So we have split our analysis in two: 1. Mrk 421 bright intervals only 2. All other blazar bright intervals (distinct optimization) Fraction of fluence vs time for the six blazars. Points from Markarian 421 are shaded red. The blue shading indicates the optimal cut while the green line shows constant fluence.

10 10 Test Analyses on Scrambled Data Results of scrambled data runs Top: distribution for a random single run. Red points were found during times of interest. Bottom: distribution of neutrinos found during times of interest from the scrambled runs.

11 12 Conclusions Periods of interest from VERITAS data for IC40 have been defined Scrambled data sets confirm Poisson behavior Waiting for collaborator approval before applying to unscrambled data Fraction of fluence vs time for the six blazars. Points from Markarian 421 are shaded red. The blue shading indicates the optimal cut while the green line shows constant fluence.

12 13 Future Work Flux-sensitive point source search protocol has been defined, can easily be extended to include IC59 Numerous projects provide regular monitoring of Mrk 421 (HAWC, Swift/BAT, FACT, etc) Can adapt search process for real time analysis Mrk-421 project with similar TeV selection and x-ray data from Swift (isolate orphan flares)